Your XH is like most WASs here: totally self-absorbed, putting their perceived need for "happiness" at the base of their "Maslowe's Hierarchy of Needs"! I saw a great slogan on a parent's bag in my school the other day. "The Search for Happiness is the Biggest Cause of Unhappiness"! Perfect!
Many of us who have been left continuously examine "What must I have done to make this happen?" Let it go. It doesn't matter. THEY were searching for something they will not find.
Great idea about getting in shape. You know I always harp on that for you! Get out and walk, Rent space in your own head and evict him....."The Warrior" that he dubbed himself! LMAO!